Solid phase extraction (SPE) and liquid chromatography separations are well known, extensively used processes. Selective extraction, selective washing and selective elution are the three fundamentals of the SPE process and a stepwise procedure is used to separate compounds of interest from impurities. In the first step, the sorbent is conditioned with a solvent or eluent. In a second step, the sample is added and washed through the sorbent. Selected components are adsorbed when the sample passes through the SPE matrix and the effluent contains the non-adsorbed components. The third step involves selective washing with solvents that are strong enough to remove impurities but weak enough to leave compounds of interest behind. The final step is to wash the matrix with a solvent that will elute the compounds of interest. In some procedures, only two steps are necessary since the compounds of interest are collected in the effluent as the sample passes through the matrix with impurities remaining on the sorbent. These basic steps are typical for SPE using reverse phase, normal phase, and ion exchange sorbents.
The present invention relates to methods of isolating biological analytes such as synthetic peptides from a sample and are particularly advantageous for purifying mixtures of synthetic peptides directly from a cleavage/deprotection mixture. In an embodiment the invention relates to a method for isolating a biological analyte from a sample, comprising the steps of precipitating a biological analyte onto a solid phase extraction device; and eluting the biological analyte off of said solid phase extraction device. In an advantageous embodiment, the liquid sample is applied onto the solid phase extraction column followed by drying of said solid phase extraction device, preferably as a thin film on the solid phase extraction device, which can be, e.g., a packed column, a coated membrane or the like.